The present invention relates to cathode ray tubes and more particularly to cathode ray tubes providing improved storage operation, improved storage target thereof and method of making such storage targets.
U.S. Pat. No. 3,531,675 discloses a cathode ray storage tube in which the storage target is provided with protrusions that have been etched from the insulating substrate and they and the surface from which they protrude are coated with a thin layer of transparent conductive metal oxide thereby defining a collector electrode. A dielectric layer is disposed onto this collector electrode and the other portions of the protrusions extend outwardly beyond the dielectric layer. This storage target is expensive to manufacture due to the etching of the substrate to form the protrusions and the subsequent formation of the dielectric layer can vary in thickness at various locations over the target due to variance in the etching that takes place. The area of the protrusions also vary due to non-uniformities of the substrate and the fabrication thereof. The etched configuration of the substrate makes it difficult to discern non-uniformities and defects of the protrusions and dielectric layer. The operating areas of the protrusions can be impaired due to phosphor adhering too far up the protrusions thereby reducing the collection efficiency.
This patent also discloses the use of frit projections adhered onto a flat surface of the insulating substrate, a thin layer of conductive material is coated onto the flat surface and frit projections whereafter disposed onto the conductive layer. It has been found in this type of target that the frit does not provide high enough projections due to frit spreading out onto the flat surface when it is melted.
U.S. Pat. application Ser. No. 356,029, filed Apr. 30, 1973, now U.S. Pat. No. 3,956,662 describes an invention which is directed to a conductive coating applied onto a smooth surface of an insulating support plate, dots or protrusions of metallic particles are provided on the conductive coating and storage dielectric is disposed on the conductive coating with the outer ends of the protrusions extending beyond the top surface of the dielectric. This target has proven satisfactory; however, it has been found that the metallic protrusions do not adhere to the conductive coating as desired and the cobalt metal particles that form the protrusions are becoming too expensive to use.